From owner-freebsd-hackers@FreeBSD.ORG  Sun Mar 15 02:45:26 2015
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115])
 (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTPS id 48FCA741
 for <freebsd-hackers@freebsd.org>; Sun, 15 Mar 2015 02:45:26 +0000 (UTC)
Received: from mail-qc0-x235.google.com (mail-qc0-x235.google.com
 [IPv6:2607:f8b0:400d:c01::235])
 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
 (Client CN "smtp.gmail.com",
 Issuer "Google Internet Authority G2" (verified OK))
 by mx1.freebsd.org (Postfix) with ESMTPS id 006C4CA0
 for <freebsd-hackers@freebsd.org>; Sun, 15 Mar 2015 02:45:26 +0000 (UTC)
Received: by qcaz10 with SMTP id z10so18696919qca.1
 for <freebsd-hackers@freebsd.org>; Sat, 14 Mar 2015 19:45:25 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113;
 h=mime-version:date:message-id:subject:from:to:content-type;
 bh=UERT2OTXE1cMxvMQG7wENZHa98UAvWN3ZrC2W5PasFc=;
 b=irnQ5WMT8OxrmZepmqKCzNPJF/+YowNLCW7ywOtaksV/RMEw+PFfEzVvZMIPO7L721
 Jk0rfcXCGray8MNaiFdwVfBUuydgAekR+BX5FS0PEQPMzPNUvOzAF1wDijZij7EklC/D
 B19Xq1Hyc23V/Hv+BaSB957IMm1xLOMrz9CfheuuHzaGh2u1kxPG3ybSY9wZi1ttsBSv
 8jSjBfor7legpxfvvvFDdUSgawOVK9TeaC+7Hr2yPQ0V9s1iqEOxGGKdBGiNXTQu78/J
 VWeRt9WULTB4WHFbbm+x3m9uuO+fSIOh1hPb6g2kyfhIABZScFE4KTw/Ko5M+MZLC9bh
 OrSg==
MIME-Version: 1.0
X-Received: by 10.141.28.78 with SMTP id f75mr71221647qhe.18.1426387525165;
 Sat, 14 Mar 2015 19:45:25 -0700 (PDT)
Received: by 10.229.24.73 with HTTP; Sat, 14 Mar 2015 19:45:25 -0700 (PDT)
Date: Sat, 14 Mar 2015 19:45:25 -0700
Message-ID: <CAF10W3zSZaH8sttrS8L3gHRNOkJEiNY1HmKXnfNmgK4TSSH56A@mail.gmail.com>
Subject: ngets() consuming 100% CPU
From: Ivan Krivonos <int0dster@gmail.com>
To: freebsd-hackers@freebsd.org
Content-Type: text/plain; charset=UTF-8
X-Content-Filtered-By: Mailman/MimeDel 2.1.18-1
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.18-1
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
 <freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-hackers>, 
 <mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers/>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
 <mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sun, 15 Mar 2015 02:45:26 -0000

Hi All,

I`ve noted that ngets() from libstand starts consuming CPU like mad when
 EOF appears on stdin. Not sure if this actually is a bug, but issue
appears
from time to time with bhyveload. Here is simpliest program allowing
 reproduce

cat > ./bget.c


#include <stdint.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/file.h>

int main()
{
        char str[512];

        for (;;) {
                ngets(str, sizeof(str));
                if (str[0] == '\n')
                        break;
        }
        return 0;
}

$ echo "balbalbalabl" | ./bget &
$

You will see bget consuming CPU in ngets() reading EOF. The patch below
fixes the problem

diff --git a/lib/libstand/gets.c b/lib/libstand/gets.c
index 7d54b00..806091a 100644
--- a/lib/libstand/gets.c
+++ b/lib/libstand/gets.c
@@ -44,8 +44,12 @@ ngets(char *buf, int n)
     int c;
     char *lp;

-    for (lp = buf;;)
-       switch (c = getchar() & 0177) {
+    for (lp = buf;;) {
+       c = getchar();
+       if (c == EOF)
+               break;
+
+       switch (c & 0177) {
        case '\n':
        case '\r':
            *lp = '\0';
@@ -79,6 +83,7 @@ ngets(char *buf, int n)
                putchar(c);
            }
        }
+    }
     /*NOTREACHED*/
 }